A substrate processing apparatus is configured to form thin films on a substrate through a chemical vapor deposition (CVD) process or an atomic layer deposition (ALD) process. The thin films formed on a substrate may include a silicon nitride film (e.g., Si3N4 film; hereinafter, in some cases referred to as a SiN film), a polycrystalline silicon film (hereinafter, in some cases referred to as a poly-Si film) and the like. Such a substrate processing apparatus is provided with a process vessel configured to contain a substrate to be processed therein, a support member for supporting the substrate inside the process vessel, and a process gas supply system for supplying a process gas into the process vessel. In the substrate processing apparatus, the substrate placed on the support member is heated to a certain temperature. If the temperature of the substrate reaches a stable state after a lapse of a predetermined period of heating time, the process gas is supplied into the process vessel so that a thin film is formed on the substrate.
If the thin film formation process is repeatedly performed, it may cause a deposited film made of SiN, poly-Si or the like to be formed on an inner wall of the process vessel or a surface of the support member. As the deposited film becomes thicker, foreign materials may be generated by peeling-off of the deposited film and may adhere on a surface of the substrate. For this reason, once a cumulative thickness of the deposited film reaches a predetermined level, a cleaning process is performed in which a cleaning gas such as ClF3, NF3, HF, F2, or the like is supplied into the process vessel to remove the deposited film by etching.
The support member may be formed of quartz (SiO2), silicon carbide (SiC), aluminum nitride (AlN), or other ceramic materials. The support member may be made of a high heat conductivity material in order to stabilize the temperature of the substrate (in a short period of time). Also, the support member may be made of a material containing a small concentration of impurities in order to prevent contaminations inside the process vessel or on the surface of the substrate.
FIG. 5 is a table showing a relationship between a heat conductivity (thermal conductivity) and a level (or concentration) of impurities contained in various kinds of materials which may be employed in manufacturing the support member. As shown in FIG. 5, the MN material has a high heat conductivity of 90 to 200 W/mK, while a concentration of impurities thereof is also high in the order of sub-% level (e.g., below 1%). As such, the MN material may not be suitable as a material of the support member in terms of preventing contaminations inside the process vessel or on the surface of the substrate. On the other hand, SiC (hereinafter, in some cases referred to as CVD-SiC), which is formed by a CVD process, has a high heat conductivity of 140 W/mK, and a concentration of impurities thereof is low in the order of ppm units. Therefore, the SiC material has a property suitable to be used as a material of the support member.
In spite of such a suitable property as described above, the SiC material has poor workability due to its high stiffness. A technique for addressing such a problem may be effectively employed in which a carbon base material or a Si-impregnated SiC base material is shape-processed in advance and then, a SiC film having a thickness of, e.g., 10 to 200 micrometer (μm) is coated by a CVD process on a surface of the carbon base material or the Si-impregnated SiC base material so that the support member is implemented with the coated base material. FIG. 7 shows a schematic cross-sectional view of a support member with a CVD-SiC film coated on the surface of the carbon base material or the Si-impregnated SiC base material. In terms of the concentration of impurities, although the carbon base material or the Si-impregnated SiC base material is not comparable to the CVD-SiC film, such a base material with the CVD-SiC film coated thereon may be used in preventing the inside of the process vessel or the surface of the substrate from being contaminated. In some cases, impurities generated by machining which is performed during the shape-process may remain left on the surface of the carbon base material or the Si-impregnated SiC base material. In such a case, since the CVD-SiC film is coated on the surface of the base material, the contamination can be restrained as described above.
However, if the aforementioned cleaning process is performed on the support member having the above-described configuration, contamination may occur inside the processing chamber or on the substrate. In other words, the CVD-SiC film is etched by cleaning gas so that the carbon base material or the Si-impregnated SiC base material, each underlying the CVD-SiC film, is exposed, which may cause contaminations inside the processing chamber or on the surface of the substrate.